{n} or {m,n} notation provides a more general way of writing regular expressions : Occurrences : Regular Expressions MySQL TUTORIALS

{n} or {m,n} notation matches many occurrences of the previous atom (or "piece") of the pattern.

m and n are integers.

1. a*: Can be written as a{0,}.
2. a+: Can be written as a{1,}.
3. a?: Can be written as a{0,1}.
4. a{n} matches exactly n instances of a.
5. a{n,} matches n or more instances of a.
6. a{m,n} matches m through n instances of a, inclusive.

m and n must be in the range from 0 to RE_DUP_MAX (default 255), inclusive.

If both m and n are given, m must be less than or equal to n.